Mammography is the process of obtaining x-ray images of the human breast for diagnosis or surgery. It involves positioning a patient's breast in a desired orientation against a cassette holder (also known as a “bucky”) of a mammography unit, compressing the breast with a compression device (e.g., a compression paddle), and then exposing the breast to x-rays to create a latent image of the breast on an image receptor. After exposure, the compression device is released. An example of the image receptor is a film in contact with an intensifying screen contained within a cassette. The cassette is inserted into the cassette holder before every image is taken and removed after every image. The film is removed from the cassette and developed to produce a radiographic image of the breast. Another type of image receptor is a solid state device, and the image is obtained electronically.
A complete mammographic study usually involves at least two x-ray exposures of each breast. One exposure is a craniocaudal view in which the breast is compressed in a superior-inferior direction, i.e., from the direction of the patient's head downward, against a tube-side surface of the cassette holder. The plane of the tube-side surface of the cassette holder is parallel to the floor and the x-ray beam is directed vertically downward. A second exposure is a lateral or oblique view in which the breast is compressed mediolaterally, i.e., from the direction of the patient's midline sidewise, against the tube-side surface of the cassette holder which is angled, along with the axis of the x-ray beam, relative to the floor.
Typically, the compression device is a compression paddle, which includes a rectangular flat plate that is attached to the mammography unit between an x-ray tube assembly and the bucky. The edges of the paddle are usually turned upward away from the bucky to provide a smooth curved surface for patient comfort. The compression paddle is usually made of thin, light-transparent, plastic that absorbs only a small fraction of the incident x-ray beam. The compression paddle is moved either manually or by power drive to apply a compression force to the breast, thereby limiting breast motion and flattening the breast against the cassette holder to a near uniform thickness to improve image quality. U.S. Pat. No. 6,049,583 issued to the present inventor discusses methods and apparatus for measuring compression force in mammography. During compression, parts of the patient's body come into contact with the compression paddle. After x-ray exposure, the compression force is released for patient comfort.
As is well known in the field, to properly position the breast, the patient's chest wall or other regions of the body, depending on the desired view, are brought into tight contact with the rigid surfaces of the cassette holder, its edges, and corners. This procedure has the effect of forcing the patent's anatomy to contour to the shape of the cassette holder, which often causes patient discomfort and pain. Oftentimes, overlapping internal structures are present within the breast tissue that can obscure their delineation in a radiographic image. As a result, it is often necessary to reposition the breast slightly in order to arrive at a diagnosis. This requires repositioning the patient for each view with the attendant discomfort due in part to repeat compressions. U.S. Pat. No. 6,850,590 by the present inventor, incorporated herein by reference, discusses methods of reshaping the breast without repositioning.
It is well known that many women find the procedure for compressing the breast to be uncomfortable and for some, even painful. Methods to provide patient comfort during this procedure involve adding cushioning material to the patient contact surfaces of the compression paddle. Examples are described in U.S. Pat. Nos. 6,577,702 and 6,968,033 issued to Lebovic et al.; and U.S. Pat. No. 6,765,984 issued to Higgins, et al. Also, U.S. Pat. No. 6,975,701 and U.S. Patent Publication No. 2006/0050844 by the present inventor, each of which is incorporated herein by reference, describe cushioning devices for compression paddles. U.S. Pat. No. 5,479,927, issued to Shmulewitz discusses a gel pad attached to the patient-contact surface of the compression paddle.
To properly position the patient's breast in a desired orientation before exposure, a technologist is guided by a light beam originating from the x-ray tube assembly that passes through a collimator and the compression paddle to illuminate the area of the bucky that will be exposed to x-rays, i.e., the imaging area. Sometimes, adding cushioning materials to compression paddles blocks the light and impedes proper positioning of the breast.
Other attempts to resolve problems with the compression paddle have included redesigning the shape of the paddle or its angulation, e.g., U.S. Pat. Nos. 4,962,515; 5,199,056; 5,506,877; 5,706,327; 6,974,255.
Angiogenesis plays an important role in the development of breast carcinoma. The use of contrast and molecular imaging agents to detect and/or treat breast cancer also relies on breast vascularity. Unfortunately, traditional mammography systems that exert static compression force on a breast that is positioned between a bucky and a compression paddle are incompatible with studies relating to blood flow during mammography screening, as the static compression force at least partially interrupts blood flow within the breast.
A recent study concluded that the use of computer-aided detection (CAD) in mammography is associated with reduced accuracy of interpretation of screening mammograms, and furthermore that the increased rate of biopsy with the use of computer-aided detection is not clearly associated with improved detection of invasive breast cancer. Fenton J J et al., N Engl J Med. 2007 Apr. 5; 356(14):1399-409.
There remains a great need for devices and methods to compress a patient's breast during mammography that can minimize or eliminate the pain and discomfort experienced by the patient. There also exists a need for devices and methods that can compress a patient's breast but that are not incompatible with studies relating to blood flow during mammography. Improvements to CAD sensitivity and specificity during mammography could reduce incidence of unnecessary biopsies, but such improvements have not yet been developed.